Radio signaling system



March 17, 1931. E. F. w. ALEXANDERSON- 1,797,039

RADIO SIGNALING SYSTEM Filed Jan. 1'7, 1922 2 Sheets-Sheet l Inventor: Ernst 'F.\/-/. NexamoL-er'aqn,

' ,M His Miiiornev.

March 1931- E. F. w. ALEXANDERSON 1,797,039

RADIO SIGNALiNG SYSTEM Filed Jan. 17, 1922 2 Sheets-Sheet 2 Inven L01":

ErnsLFIWAI exrmderson;

e MM His AtLoT-"ne' Patented Mar. 17, 1931 airs-o STATES PATENT OFFICE ERNST F. W. ALEXANDERSON, OF SCHENECTADY, NEVI' YORK, ASSIGNOR T GENERAL ELECTRIC COMPANY, A CORPORATION OF -NEW-YORK RADIO SIGNALING SYSTEM Application filed January 17, 1922, Serial No. 529,957, and in Great Britain February 15, 1921.

The present invention relates to radio signaling systems, and more particularly to socalled multiplex systems of transmission.

The object of my invention is to provide a simple and efficient method and apparatus whereby it will be possible to simultaneously radiate, from a central station and from a plurality of radiating antennae situated in close proximity to one another, a plurality of different wave lengths.

If a single aerial is to be tuned for two frequencies and two waves of equal amplitude are to be transmitted simultaneously, it is obvious that the combined radiation from the aerial will be of a pulsating nature with a beat corresponding to the difierence between the two frequencies. The combined radiation will be maximum when the two radiations are in phase and the radiation will be 29 zero when the two combined radiations are of opposite phase. There will thus be moments when there is no radiation and no oscillating energy in the radiating antenna. In order to make it possible to produce a radiation of a rapid beat frequency insuch a system it is necessary to store the oscillating energy in a non-radiating circuit during the time when no radiation takes place so that this stored energy can again be transferred 30 to the radiating circuit during the moments when radiation takes place. One way which I have proposed for producing this effect is to couple to the antenna an artificial non-radiating circuit in' such a way that the oscillating energy may be transferred between this circuit and the antenna. In this way a single antenna may be constructed which is capable of radiating at two wave lengths simultaneously. In case largepowers are to be radiated the system described has the disadvantage that a large number of large condensers would be required for the energy storage circuit and the cost of installation would be excessive.

In accordance with my present invention this difficulty is overcome by providing a separate antenna for each of the wave lengths to be radiated and coupling these antennae together by means of an inductance so proportioned as to neutralize the mutual capacity between the antennae at a particular wave len 'th. The wave length at which the inntuaI capacity is neutralized may be a wave length intermediate the two wave lengths to be radiated, or it may be the wave length at which one of the antennae is to be operated. In the case of two antennae each supplied by a source of high frequency energy at different frequencies, the mutual capacity between the antennae may be approximately neutrallzed by an inductance inductively connected between them. This coupling need not necessarily be conductive as a magnetic coupling may be employed if desired. If the induc tance is adjusted to neutralize the mutual capacity between the antennae at the frequency of one of them, that antennae will oscillate freely practically as if the other antenna did not exist. At the wave length to be radiated from the other antenna the capacitycoupling between the two antennae will not be neutralized and the tuning therefore of that antenna must be modified so as to compensate for the electrostatic coupling which still exists between it and the first antenna.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims, my lnvention itself however both as to its organization and method of operation will best be understood by reference to the following description taken in connection with the accompanying drawing in which Figs. 1, 2, and 3 illustrate diagrammatically three ways whereby my invention may be carried into effect.

As indicated in the drawing, two antennae l and 2 are supplied by separate sources of high frequency current 3 and 4, which may be high frequency alternators, or any other desired source. The usual tuning coils 5 and 6 are inserted in the antenna circuits. The antennae 1 and 2 are preferably of the multiple tuned type, as described in my Patent 1,360,167, November 23, 1920. The high frequency sources deliver energy at different frequencies and it may be assumed that the frequency of the source 4 is less than that of the source 3, and that antenna 2 radiates a longer wave length than antenna 1. The two antennae are coupled by an inductance 7 which is adjusted so that the electrostatic coupling between the two antennae is neutralized for the frequency impressed upon the antenna 1. Inductance 7 is indicated in the drawing as directly connectedbetween the two aerials. This is not essential as a magnetic coupling may be employed as well. For example, tuning coils 5 and 6 maybe coupled so that the electrostatic coupling between the aerials is neutralized for a particular fre quency. Preferably, however, the inductive coupling for neutralizing the electrostatic coupling will be independent of the tuning coils 5 and 6. The inductive coupling may be desirable in cases where the mutual capacity between the antenna is so low that an excessively high inductance would be required for neutralization by direct coupling. With this ar *angement each antenna will oscillate at its own natural frequency. So far as antenna 1 is concerned it will oscillate practically as if the antenna 2 did not exist because the shunt or differential circuit made up of inductance 7 and the electrostatic ca pacity between the antennm is tuned to the frequency of the antenna 1. Since, however, the capacity and inductance are neutralized at one frequency only the capacity coupling between the two antennae is not quite neutralized for the frequency radiated from the antenna 2.

F or the control of the radiated energy for the transmission of signals 1 have indicated magnetic amplifiers S and 9 connected in a well known manner, as set forth in my Patent 1,328,610, January 20, 1920, these magnetic amplifiers being connected in shunt across the high frequency sources 3 and 4. With this arrangement the effect of the oscillating energy of the antenna 2 upon the control of the energy in antenna 1 may be neutralized by a coupling transformer 12, the primary of which is in series with antenna 2 and the secondary of which is in series with amplitier 8. This transformer may beso adjusted as to impress upon the circuit of amplifier 8 a voltage equal and opposite to that caused by the current produced in the antenna 1 by reason of the electrostatic coupling between the two antennae. With this arrangement no current from source a will flow through amplifier 8 at any time and the variation of the tuning of either antennae by means of the magnetic amplifier associated therewith will have no effect upon the tuning of the other antenna.

In Fig. 2,1 have indicated a further modification of my invention in which the desired compensation may be secured by a combination of direct and electromagnetic coupling. In this case the direct coupling coil 7 is supplemented by a variable magnetic coupling transformer 13.. The mutual capacitybetween the two antennae is in this case indicated by the dotted condenser 14. With this arrangement the coil 7 and transformer 13 may be so adjusted that by their conjoint action they will transfer enough energy from one antenna to the other to neutralize the effect of the energy transferred by the capacity 14 at the frequency of one antenna. Then in case the other antenna is of a lower frequency, the energy transferred at that frequency by the coupling coil 7 will increase while the energy transferred by the'coupling transformer 13 will decrease. By proper proportioning of the two couplings however the decrease in energy transferred by transformer 13 may be made enough greater than the increase in energy transferred by coil 7 to compensate for the decreased transferthrough capacity 14 and the sum of the two may be made equal to the energy transferred through capacity 14- so that neutralization is also accomplished for the lower frequency.

This system for partially neutralizing the capacity coupling between the two antennae may be extended to a radiating system made up of three or more antenna units intended for radiating a corresponding number of signals. If, for example, three waves are to be radiated the three antennae may be interconnected by inductances 15, 16 and 17 as indicated in Fig. 3 so that each differential antenna circuit may be tuned for the intermediate wave lengths, each intermediate circuit being entirely detached from the other two. With reference to the antenna intended to radiate with the lowest frequency the differential circuits will'have the effect of inductances shunted from the aerial to the other two antennae. The path from the aerial to ground of each of the other antennae will also have the efiect of an inductance at that lower frequency. The low frequency aerial will thus in effect be tuned by its own inductance to ground and two inductive shunt circuits, each shunt consisting of the effective inductance of the difierential circuit in series with the effective inductance of one of the other two antennae, the combined inductances of these three shunted inductive circuits should be equivalent to the inductance needed to tune the low frequency aerial at its desired wave length. F or effecting a complete neutralization in the case of three or more antennae, the methods illustrated in Figs. 1 and 2 may be employed in connection with the direct magnetic coupling.

With respect to the high frequency aerial, in the case of two antennae and the oscillating circuit of the other antennae, the differential circuit will have the effect of capacity shunts which are in series with the oscillating circuits of the high frequency aerial. The tuning inductance to be applied to the high frequency aerial then must be such that in combination with the shunt capacity circuits it gives a resulting inductance which is the desired inductance for tuning the high frequency aerial at the desired wave length. The same considerations will apply in the case of three or more aerials, there being for each antenna as many shunt capacity or inductance circuits as the number of additional antennae of lower or higher frequency respectively.

While I have shown and described the preferred embodiments of my invention, it will be apparent that my invention is by no means limited to the specific arrangements shown and described as many modifications in the manner in whichthe undesired reactions between the different antennae may be neutralized may be made without departing from the scope of my invention as set forth in the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. The combination in a radio signaling system'of two transmi ting antennae in proximity, a source of high frequency energy of one frequency connected to one antenna, a source of high frequency energy of a different frequency connected to the other antenna, aconductive connection between said antennae having sufficient inductance substantially to neutralize the mutual capacity existing between said antennae at the frequency of the source connected to one of said antennae, and amagnetic coupling interposed between said antennae for transferring energy of the frequency of the source connected to tie other antennae to said one antenna in phase opposition to energy transferred to said one antenna from said other antennae through mutual coupling existing between said antennae.

2. The combination in aradio signaling system of two transmitting antennae in proX- imity, a source of high frequency energy of one frequency connected to one antenna, a source of high frequency energy of a different frequency connected to the other antenna,

an inductance connected between the two an-,

tennae for neutralizing the mutual capacity between them at the frequency of one of the sources, and a magnetic coupling between the two antennae for preventing an undesired effect upon the antenna connected to the source of that frequency from currents-set up in the other antenna.

3. The combination in a radio signaling system of two transmitting antennae inpronimity, a source of high frequency energy of one frequency connected to one antenna, a source of high frequency energy of a different frequency connected to the other antenna, a coil connected betwen the two antennas having inductance suiiicient to neutralize the mutual capacity between them at the frequency of one of the sources, a shunt circuit includ ing a signal device connected across said one source, and a transformer connected between the other antenna and said shunt circuit for preventing an undesired eflect upon the antenna connected to the source having said shunt from currents set up in the other antenna.

i. The combination in a radio signaling system of two transmitting antennae in proX- imity, a source of high frequency energy of one frequency connected to one antenna, a source of high frequency energy of a different frequency connected to the other antenna, a 

